Yes combine the two 1099-Ss and enter it as one sale. You could attach a statement, they are usually ignored and lost and you won't be able to e-file. Just keep good records, in case of an IRS inquiry.
Although you situation is certainly unique; a similar and more frequent case is where the homeowner splits the lot into two parcels and sells them separately. Both parcels count as sale of the principal residence, even if sold at different times.
